Charged Clusters of C and Au or Cu: Evidence for Stable Sizes and Specific Dissociation Channels.

We have doped helium nanodroplets with C and either gold or copper. Positively or negatively charged (C) M ions (M = Au or Cu) containing up to ≈10 fullerenes and ≈20 metal atoms are formed by electron ionization. The abundance distributions extracted from high-resolution mass spectra reveal several local anomalies. The sizes of the four most stable (C) Au ions identified in previous calculations for small values of m and n ( m ≤ 2 and n ≤ 2, or m = 1 and n = 3) agree with local maxima in the abundance distributions. Our data suggest the existence of several other relatively stable ions including (C)Au and (C)Au. Another feature, namely the absence of bare (C), confirms the prediction that (C)M dissociates by loss of C rather than loss of M. The experimental data also reveal the preference for loss of (charged or neutral) C over loss of a metal atom from some larger species such as (C)M. In contrast to these similarities between Au and Cu, the abundance distributions of (C)Au and (C)Cu are markedly different. In this discussion, we emphasize the similarities and differences between anions and cations, and between gold and copper. Also noteworthy is the observation of dianions (C) Au for m = 2, 4, and 6.